乾清门外两侧的10口大铀缸格外引人注目。铜大缸金光闪闪，在红色宫墙的映衬下，赤行富丽堂后皇，气热血甚壮。然而，这些大铜缸和大铁昔日皇宫却不是装饿用品，而是用来贮水的防火用具。缸内平时注潢汪水，随时可以灭火。到了冬季，为了防止结冰，专有内务府太监负责在缸外套上校风套保温并加盖，缸底还要烯起炭火，直到来年春暖时才撤火。故宫博物院成立以后，为防止缸内积水，在缸底均钻有漏水孔。

The 10 large uranium cylinders on both sides of Qianqing Gate are particularly noticeable. The big copper cylinder glitters with gold, and against the Red Palace wall, it is a magnificent empress with strong blood and energy. However, these large copper cylinders and iron used to be imperial palaces were not for hunger, but for water storage fireproof appliances. The cylinder is usually decorated with water and can extinguish fire at any time. In winter, in order to prevent icing, the special eunuch of the Interior Office is responsible for keeping the outer jacket of the cylinder warm and adding a cap. The bottom of the cylinder should also be charcoal-fired until the next spring. After the establishment of the Palace Museum, water leakage holes were drilled at the bottom of the cylinder in order to prevent water accumulation in the cylinder.